This invention relates generally to mattress foundation structures utilizing non-coil springs. More particularly, this invention relates to a non-coil box spring assembly having spring modules with improved spring installation capabilities.
Box spring assemblies using non-coil support springs or spring modules have been known since about 1964, the first such spring assembly known to Applicant was disclosed in U.S. Pat. No. 3,286,281. Box spring assembles of this general type are advantageous (with respect to conventional coil box spring assemblies) because they provide a stiffer foundation for the mattress and contain a reduced amount of spring wire. Additionally, these non-coil box spring assemblies offer prolonged service life, easy assembly and reduced manufacturing costs.
Mattress foundation structures which use non-springs, often referred to as wire forms, offer still further increases in stiffness and support, especially around the perimeter of the foundation structure. The stiff perimeter prevents significant localized deflection of the mattress and foundation structure when a person is sitting on the edge of the bed. This eliminates the "sliding off" feeling typically associated with less stiff or soft mattress and box spring assemblies.
While wire form mattress foundation structures exhibit benefits with respect to perimeter stiffness, they also are inherently limited as a result of their increased stiffness. While not apparent during normal use conditions, this limitation arises under "normal" abuse conditions such as sudden impact loads resulting from a person jumping, diving or falling onto the bed. The increased load applied to the foundation structure under such a condition, coupled with the limited deformation resistance of the wire form itself, often results in the wire form becoming permanently set and damaged.
Both non-coil spring modules and wire forms are mounted (hereinafter referred to as spring modules) so that they support a wire grid or support deck above a frame. These three elements (the deck, the spring modules and the frame) make up the principal components of a box spring assembly. Two methods are generally used to attach the spring modules to the deck.
In the first method, self-securing clips extend around portions of both the deck and the spring module to hold them together. Use of the clips, however, is labor intensive and adds numerous parts to the overall assembly since each spring module typically requires at least two clips. Another inconvenience is that the clips further increase the inventory which must be kept on hand at the production facility.
The second method generally used to secure spring modules to the support deck involves interweaving a deck attaching portion of the spring module with the wires of the support deck. When interwoven in this fashion a long or cross wire extends over and under several portions of the deck attaching portion. To attach a spring module in this manner, the downwardly extending or yieldable portions of the spring module are positioned on opposite sides of one cross wire so that the deck attaching portion extends generally diagonally across at least two of the long wires and the cross wire. The spring module is then rotated about a vertical axis to bring the end sections of the deck attaching portion beneath the cross wire. This effectively clamps the spring module onto the cross wire. The securement is called "interwoven" since the cross wire extends over one end, under a middle section and over the other end of the deck attaching portion. Because of the diagonal initial mounting, it is often initially necessary for the yieldable portions of the spring module to be spread outwardly to allow the spring module to fit diagonally over the required number of long wires.
It is an object of the present invention to simplify the installation of spring modules into a box spring assembly. Installation is improved by eliminating the use of clips and the need for the spring module to be rotated so as to achieve the interwoven attachment as mentioned above. A related object of the present invention is to provide a spring module with a construction that allows the spring module to attach to the deck through a simplified, axial movement of the entire module.
It is also an object of the present invention to provide a box spring assembly which simulates a non-spring mattress foundation structure in terms of effective firmness while improving deformation resistance in the spring module.
In achieving the above and other objects, the present invention provides a box spring assembly having a rectangular frame made up of side rails, end rails and a plurality of cross rails. The cross rails are generally parallel to each other and the end rails and are substantially perpendicular to the side rails. A welded wire grid or support deck is supported, generally horizontally, a predetermined distance above the frame. The support deck includes a border wire that defines the perimeter of the deck and a number of straight wires, some of which extend lengthwise of the frame and others of which extend crosswise of the frame.
To yieldably support the deck above the frame, a number of unitarily formed support springs or modules extend between the deck and the frame. Each of the support springs is formed of spring wire and has a body made up of two side-by-side yieldable sections. While they may have a variety of configurations, in the illustrated embodiment the yieldable sections each include coaxial upper and lower column portions which are connected together by a middle portion. The configuration of the middle portion allows the yieldable section to bend in a substantially vertical plane in response to loads applied to the assembly. This deformation provides the box spring assembly with the desired amount of deformation resistance. In preferred form, the middle portions are arcuate and generally semi-circular in shape. This avoids any areas of stress concentration that might weaken the support springs during repeated response to applied loads and enables the support spring to resist normal abuse conditions without developing a permanent set.
The two yieldable sections of each support spring are connected together at their upper ends by a deck attaching section which coacts with at least one of the straight wires to secure the support spring to the support deck. The deck attaching section includes a pair of end bars which are interconnected by a cross bar that extends between immediately opposing ends of the end bars. The cross bar is provided with an axial extension, generally in its middle, that has a length about the same as that of the end bars. The extension extends from the cross bar in the same direction as the end bars.
To mount the support spring of the present invention to the support deck, the support spring is positioned to one side of a crosswise straight wire so that the deck attaching portion spans a number of the lengthwise straight wires. The entire support spring is then moved in an axial direction along the support deck so that both of the end bars are positioned beneath the crosswise straight wire. The middle extension of the cross bar remains positioned across the top of the crosswise straight wire thereby clamping the support spring to the deck and achieving the interwoven construction mentioned above.
Additional benefits and advantages of the present invention will become apparent to those skilled in the art to which this invention relates from the subsequent description of the preferred embodiments and the appended claims taken in conjunction with the accompanying drawings.